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Microsoft plays with small, sleepy servers

Like kittens, only crunchier

The Cloud Computing Futures (CCF) research unit at Microsoft, officially launched this week at the TechFest event in Redmond but secretly in existence for more than a year, showed off a number of projects at the event, two of which relate to servers.

One demonstrated the use of low-powered processors and small form-factor motherboards to do work that might otherwise be done by 1U, 2U, and 4U x64 or RISC servers common in data centers.

Jim Larus, director of software architecture at CCF, said that his group was researching how to support large-scale Microsoft services using netbook-class processors. To do so, his team built an experimental half-rack with 50 small form-factor boards equipped with Intel Atom processors.

The boards are mounted vertically on two sets of sliding rails in a five-by-five configuration. The vertical mounting allows heated air to easily flow up off the components and out of the rack. To facilitate air movement and heat dissipation, none of the boards are in an enclosure.

There only fans on the server boards are on the processors, cutting down on power. In the demo set-up, the five servers in each line appeared to be sharing the same 450-watt power supply mounted on the front of the rails.

Netbook-class processors provide big-iron performance

In a statement detailing this low-power server project, Dan Reed, Microsoft's director of scalable and multicore systems and in charge of the CCF effort, provided some feeds and speeds of the Atom rack running Web 2.0-style workloads. For example, the Atom server processors consumed about 5 watts of juice, compared to 50 to 100 watts for the typical x64 processors.

Although performance for such machines is not high, you make it up in volume - which you can do with these kinds of workloads. More important, the Atom chip's idle states allow it to sleep or hibernate when not in use. For an entire Atom-based server board, power consumption ranges from 28 to 34 watts when running real workloads. When it hibernates, however, power consumption drops down to 3 or 4 watts. Considering that servers can frequently be idle, the power savings can be considerable.

Idle states may be power-savers, but data centers have service-level agreements they must maintain - customers get cranky if information doesn't just pop up at the click of a mouse. Another server-related project Microsoft Research, Marlowe, addresses this issue.

According to the Marlowe spec sheet (PDF), processors in a cluster are running at about 25 per cent at any given time, even when running large cloud-style applications. This means that 75 per cent of their cycles are doing nothing but generating heat.

Marlowe shifts some servers into idle, thus driving up the utilization rates of the remaining boxes. But it's not just an on-off issue. The Marlowe system has to perform predictive capacity-planning so that when workloads increase the needed servers have already been activated.

"This problem has two interesting challenges," Reed explained. "The first is to estimate how many processors are necessary to handle a given workload by responding to every request in a timely manner. By analogy, how many checkout clerks should be at the cash registers?

"The second is to anticipate the workload in the near future, since it takes 5 to 15 seconds to awaken a processor from sleep and 30 to 45 seconds from hibernate. The system needs to hold some processors in reserve and to anticipate the workload 5 to 45 seconds in the future to ensure that sufficient servers are available."

To solve this, Marlowe takes regular measurements of CPU use, response time, and energy consumption of the experimental rack of Atom servers, and uses past trends to estimate future workloads. Microsoft tested the machines using its own Live Search benchmark with a 1GB index.

The CCF team has also performed tests in conjunction with Microsoft's Hotmail unit. Using something called the Cooperative Expendable Micro-Slice Servers prototype - which sounds like the cookie-sheet servers that Rackable Systems launched in January - they were able to show that power consumption can be far less than that of standard servers while providing the same quality of service.